1. Field of the Invention
The present invention relates generally to interfaces or accessories for facilitating computer communications using a modem and, more specifically, to such a device that couples the modem to the telephone line via the handset jack of a telephone instrument and receives power from a bus connector on the computer.
2. Description of the Related Art
A computer modem cannot easily be connected to a digital or PBX-type telephone system. The problem is described in U.S. Pat. No. 4,907,267, issued to Gutzmer, entitled xe2x80x9cMODEM INTERFACE DEVICE.xe2x80x9d In a PBX telephone system, multiple lines are serviced by a central controller. It is difficult to achieve dedicated line service for a modem because the telephone line to which a particular telephone instrument is connected carries digital line selection information and power in addition to the audio frequency communication signal of the handset. To solve this problem, the above-referenced U.S. patent describes a solution in which a modem is connected to the telephone system via the handset jack of the telephone instrument base unit. The patent describes an interface device that allows a user to switch between voice and data communication. To use the interface device, both the modem and the handset that was unplugged from the telephone instrument are plugged into the device. The device is then plugged into the handset jack of the telephone instrument base. The device has a switch that allows the user to selectively connect either the handset or the modem to the handset jack. The interface device converts the two-wire modem connection to the four-wire handset connection using a transformer. The transformer also provides impedance matching. K{overscore (o)}nexx of San Diego, Calif. produces a line of modem interface products based upon this concept.
The above-described modem interface devices are most commonly used with portable or notebook computers by travelers in hotel rooms and other locations having digital or PBX-type telephones. The traveler must carry the device along with his computer and other accessories. Accordingly, it would be desirable to minimize the size and weight of such a device. A battery or AC wall outlet adapter is typically included to power the internal circuitry of the device and to supply power to the modem. A modem normally uses loop current it receives from a telephone jack, but when the telephone jack is replaced with the interface device, a separate power source must be provided. An internal battery necessitates an enclosure large enough to contain it and adds weight to the device. An AC adapter is bulky and inconvenient for the traveler to store and carry along with the computer.
It would be desirable to miniaturize a modem interface device by minimizing the extent of its power supply. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.
The present invention relates to connecting a modem interface device to a computer such that the device is powered via a power signal received from a bus port of the computer. The computer is preferably a portable computer. The bus port can be, for example, a universal serial bus (USB) port, a RS-232 port, or a PS-2 port. The modem interface device has a telephone base connector, a modem connector, a power connector, a two-to-four-wire converter circuit, and a power distribution circuit. The two-to-four-wire converter circuit bidirectionally couples signals between the telephone base connector and the modem connector. The power distribution circuit receives electrical power from the power connector and supplies power to the two-to-four-wire converter circuit and the modem.
In accordance with the method of the present invention, a user connects the modem connector to a modem communication port of the computer. The user also connects the telephone base connector to the handset jack of the telephone instrument base. Importantly, the user further connects the power connector to the bus port of the computer. The bus port has power and data signals, but only the power signals and not the data signals are coupled into the power connector of the device. In other words, the device uses the bus port not for its normal purpose of data communication with the computer but rather only for the purpose of tapping into its power signals. Because the device uses the power signals provided by the bus port, it does not need a battery or AC adapter to supply power. The device can therefore be made smaller in size and lighter in weight than prior modem interface devices.
The foregoing, together with other features and advantages of the present invention, will become more apparent when referring to the following specification, claims, and accompanying drawings.